Polydextrose is a water-soluble, low calorie non-cariogenic bulking agent. It is a randomly cross-linked glucan polymer produced through the acid-catalyzed condensation of glucose. U.S. Pat. Nos. 3,766,165 and 3,876,794 to Rennhard detail the preparation of polymeric glucose and maltose products by anhydrous melt polymerization using non-volatile, edible organic polycarboxylic acids such as citric acid as catalysts, cross-linking agents or polymerization activators.
Polydextrose is an essentially non-nutritive carbohydrate (approximately 1 calorie/gram) substitute. It provides a substitute for sugar and has many of the desired technological properties of sugar, but does not have the sweetness. This non-sweet bulking capability is advantageous where conventional sugar-based compositions have proven to be too sweet. Moreover, this non-sweet bulking capability is especially advantageous when used in combination with high intensity sweeteners to provide low-calorie food products having the desirable texture of conventional sugar-containing food products without the calories associated with the sugar.
Polydextrose is commercially available in three forms, Polydextrose A, an amorphous, slightly acid fusible powder, Polydextrose N, a neutralized, light-colored 70% solution of Polydextrose A, and Polydextrose K, a neutralized powder form of Polydextrose A. These are produced by the Pfizer Co., New York, N.Y. As the polymerization process produces a mixture of polysaccharides and saccharide residuals, none of these products is a pure polydextrose product. All of these polydextrose products include a variety of residual compounds, such as glucose, sorbitol, citric acid and other compounds which contribute to the taste, color and caloric value of these products. In addition, all of the polydextrose products also include other low molecular weight compounds such as 1,6-anhydroglucose (levoglucosan) and 5-hydroxymethylfur-fural and a series of furaldehyde derivatives which also contribute a bitter taste and musty off-flavor. Although these low molecular weight compounds are found in polydextrose products only in small amounts (1,6-anhydroglucose, about 4%, bitter taste) (5-hydroxmethylfurfural, about 0.1 PPM, musty off-flavor), those amounts are significant enough to negatively impact on the usefulness of polydextrose in most food products when polydextrose is present in medium to high levels.
U.S. Pat. No. 4,622,233 to Torres discloses a first method of treating polydextrose by decolorizing with a bleaching agent and thereafter purifying the decolorized material. A further method disclosed and claimed in the Torres '233 disclosure for reducing color, glucose content and anhydroglucose content of Type A polydextrose includes the following steps: (a) contacting a 60-70% (W/W) aqueous solution of polydextrose Type A with a food-approved bleaching agent at a temperature of 25.degree.-90.degree. C. and a pH of about 2.5 to about 9.0; (b) adjusting the pH of the product of step (a), if about 7.0, to about 6.0; (c) adding one or more of the solvents selected from the group consisting of methanol, ethanol and ethylacetate such that said solvent includes 50-80% (W/W) of the mixture; and (d) filtering the final product, and, if desired, drying. The Torres '233 patent however, relates decoloration to purification which is not necessary. Moreover, decoloration in this manner can be an undesired process requirement and condition which produces its own additional problems. For example, when the polydextrose purified by the Torres '233 method is subjected to high heating, such as in cooking, the coloring returns to the substance. In addition, the bleaching step leaves undesirable residual chemicals which are difficult to remove. Furthermore, extra steps are required by Torres which require additional time, handling, and energy.
U.S. Pat. application Ser. No. 043,793, filed Apr. 29, 1987, entitled "Method of Purifying Polydextrose and Composition Containing Same" and assigned to Warner-Lambert Company, assignee of the present application, discloses a process for providing a purified, unbleached polydextrose product wherein an aqueous solution of polydextrose in a concentration of from about 10% to about 90% is intimately contacted with a polar organic solvent such as ethanol or acetone. The ratio of polydextrose to solvent is from about 5% to about 45% by weight of polydextrose to about 35% to about 85% by weight of solvent. The mixture is then allowed to equilibrate to form a substantially contaminant-containing fraction and a substantially polydextrose-containing fraction. The fractions are then separated for use of the polydextrose-containing fraction.
Co-pending U.S. Pat. application Ser. No. 193,961 filed on May 13, 1988 entitled "Purification of Polydextrose by Reverse Osmosis" also assigned to the Warner-Lambert Company discloses a process and purified polydextrose composition produced thereby wherein low molecular weight compounds such as 1,6-anhydroglucose and numerous furaldehyde derivatives are removed by modified reverse osmosis techniques. These small molecular weight compounds contribute to the musty, acidic off-tastes prevalent in the commercially available product and their removal results in a superior product with a cleaner taste.
None of the above processes or products successfully removed all of the residual contaminants that remain from the manufacturing process, however. It is an object of the present invention to produce a polydextrose composition for use in foodstuffs that is substantially free of the bitter, musty off-tastes associated with the commercially available product. It is a further object of the present invention, so produce a polydextrose composition that is decolorized through the removal of these contaminants to produce a more visually aesthetic product. More specifically, it is the object of the present invention to purify polydextrose through the use of ion-exchange which surprisingly removed most of the bitter and musty off-tastes which appear to be associated with compounds that bind to the ion exchange resins. It was found that these compounds are intimately associated with the polydextrose polymer to the extent that they have been heretofore unknown. Their removal not only results in a superior polydextrose composition with a cleaner, non-bitter taste but at the same time decolorizes the composition thereby enhancing its aesthetic value in its use in various food products.